1. Field of the Invention
The present invention generally relates to stress relaxation of a silicon nitride dielectric film and selective silicon nitride phase removal of the same. More particularly, the invention relates to methods for depositing a porous silicon nitride film as an etch mask and removing a sacrificial inter-level dielectric (ILD) silicon nitride layer through the porous film silicon nitride film.
2. Description of the Related Art
There are many materials that are low-K materials (a small dielectric constant relative to silicon dioxide), with the lowest K being porous materials or materials capable of forming air bridges/gaps. In an etching process, dielectric caps are formed over an interconnect layer that will subsequently have a porosity that will allow evacuation of a material that resides between conductors.
Methods to create an air bridge/gap utilize a porous spin-on material, self assembly spin-on materials, or a combination of lithography and reactive ion etching (RIE) materials.
Some porous spin-on materials are inherently weak, and lead to structural failure. Some self assembly spin-on materials have to be removed after a lower cap layer has been RIE'd through and an ability of such a material to self-assemble is dependent on a thickness of a polymer which does not lend itself well if there is topography on a wafer. Lithography and RIE materials have to overcome overlay of dimension specifications. For example, if line/space dimensions are near a lithography minimum limit there would be no offset in an overlay tolerance.